1. Field of the Invention
This invention is directed to improved applicators and methods for applying adhesives, and more particularly for medical adhesives. It provides for the accurate application of small amounts of adhesive in specific spots to create strong point bonds analogous to spot welds. In addition, it allows for the application of a sealant layer over the area that has been bonded, thereby permitting flexible sealing of the adhered surfaces.
It is expected to be especially useful in closure of long wounds in mammalian tissue, such as surgical incisions or traumatic lacerations.
2. State of the Art
Surgical incisions or lacerations are currently closed by sutures, staples, adhesive strips, or liquid tissue adhesives. Sutures, staples, and adhesive strips have been widely used for many years, and tissue adhesives have recently received significant acceptance with the launch of DERMABOND™ by J&J in the USA, and LiquiBand and other products in Europe. Tissue adhesives are typically applied as a thin line or wide swath along the line of the wound after the skin edges have been brought together (approximated). The edges of the wound then have to be held together while the adhesive sets. One of the advantages of tissue adhesives over the older forms of wound closure is that they both close and also seal the wound to allow fluid retention and keep out infectious agents. This may allow the patient to bathe almost immediately without fear of blood loss or infection.
A tissue adhesive is typically a low viscosity liquid that has a high affinity for tissue and wets it very easily. The applicators are typically tubes or ampoules with wide tips that have to be squeezed by the user to expel the adhesive for application. The release of the low viscosity fluid is frequently not well controlled, and can lead to flow of the adhesive into unwanted areas where it can cause unwanted adhesions. There have been many reported cases where adhesive has run into a patient's eyes or where the practitioner had glued his or her glove or instruments to the patient because of poor control of the application of the adhesive. In addition to this, strong tissue adhesives tend to be inflexible, whereas flexible tissue adhesives tend to give weaker bonds. Therefore wound closure tissue adhesives have tended to be a compromise between flexibility and bond strength.
Typical of the state of the art is DERMABOND™, which is manufactured by Closure Corporation and sold by the Ethicon Division of J&J. This product is 2-octyl cyanoacrylate presented in a plastic applicator which contains a crushable glass ampoule. The end of the applicator contains a porous spherical tip approximately 5/16″ in diameter through which the adhesive is applied after the internal glass ampoule is crushed. The adhesive is low viscosity, typically less than 10 cps, and rapidly wets mammalian skin, allowing it to run freely across the skin. Application of tissue adhesive from this tip is difficult to control. The directions of DERMABOND™ instruct the user to “Approximate wound edges with gloved fingers or sterile forceps. Slowly apply the liquid DERMABOND™ adhesive in multiple (at least 3) thin layers to the surface of the approximated wound edges using a gentle brushing motion. Wait approximately 30 seconds between applications or layers. Maintain manual approximation of the wound edges for approximately 60 seconds after the final layer.” The adhesive layer formed by this method is typically ¼ inch or more wide and quite thick due to the application of three layers. The width and thickness of this layer make the layer stiff despite the fact that 2-octyl cyanoacrylate has a lower modulus than the lower homologues such as ethyl, butyl and hexyl cyanoacrylate. The technique does not lend itself to closure of incisions or lacerations longer than a few centimeters because the wound edges have to be entirely approximated before applying the layers of adhesive.
More recently, some practitioners have adopted a procedure of “spot welding” a wound with tissue adhesives by applying tiny spots of adhesive at intervals along a wound. In this fashion they only have to approximate the wound edges at the spot they are joining and they can close much longer wounds. Once the wound has been appropriately closed, the practitioner can seal the wound by running a thin line of tissue adhesive along the length of the wound. This advance in wound closure technique is possible because of strong, fast-setting adhesives, which can be applied accurately in very small quantities. However, the strong, fast-setting adhesives tend to be stiff and the sealant line formed from this adhesive may render the wound uncomfortable.